SCIENCE OF NHL HOCKEY: Newton’s Three Laws of Motion (Grades 5-8)

Objective:

1.Students will design and carry out a demonstration of Newton’s first law of motion.
2.Students will design and carry out an investigation of Newton’s second law of motion.
3.Students will design and carry out a demonstration of the conservation of momentum and explain its relation to Newton’s third law of motion.

Introduction Notes:

Science of NHL Hockey:Newton’s Three Laws of Motion

Subject Area: Physical Science

Grade Level: 5–8 (Physical Science)

Lesson Title:Newton’s Three Laws of Motion

National Science Education Standards:

Science as Inquiry:5–8

Motions and Forces: 5–8

Suggested Prior Knowledge: concepts of mass, velocity, and acceleration; lab techniques of measuring mass, distance, and time. Note that students might more easily grasp the concepts in this video if they have already viewed the video Kinematics.

Purpose: This video focuses on the actions involved in playing the game of hockey. Although all sports are subject to Newton’s three laws of motion in one way or another, hockey shows especially clear examples. The activity will help students to understand Newton’s three laws of motion and how they relate to the conservation of momentum.

Key Vocabulary:

conservation of momentum—constancy of the total moment of a closed system; derived from Newton’s third law.

impulse—force applied over a time interval; equal to the change in momentum, or the product of mass and change in velocity, of an object the force acts on.

inertia—resistance to a change in motion of a moving object or a stationary object.

momentum—the product of an object’s mass and its velocity.

Newton’s first law of motion—Objects remain at rest or in motion with a constant speed and direction unless acted upon by a force.

Newton’s second law of motion—The net force applied to an object is equal to the product of the object’s mass and its acceleration; F = ma (net force = mass× acceleration).

Newton’s third law of motion—Every action has an equal but opposite reaction. For instance, in a collision between two objects, the forces acting are equal in magnitude and opposite in directions: F1 = –F2.

Objectives:

Students will design and carry out a demonstration of Newton’s first law of motion.

Students will design and carry out an investigation of Newton’s second law of motion.

Students will design and carry out a demonstration of the conservation of momentum and explain its relation to Newton’s third law of motion.

Materials:

- Safety goggles

- Metal toy car

- Book

- Hockey puck or coins

- Skateboard

- Bricks

- Spring scale

- Stopwatches

- Meter stick

- Tape or markers

- Newton’s cradle (or equivalent)

Procedure:

1. After students view the video, discuss with them Newton’s three laws of motion. Have volunteers summarize the presentation of inertia and conservation of momentum in the video, and point out examples of the three laws as they view the video again—perhaps in slow motion or with the sound muted. Emphasize to students that a hockey puck obeys Newton’s laws, just as colliding hockey players do. (The same is true for a ball in other sports, such as basketball, soccer, golf, or jai alai.) Focus on exploring each of the laws, using the following questions to start the discussion:

How might a struck hockey puck demonstrate Newton’s first law of motion?

How might two hockey players demonstrate Newton’s second law of motion?

According to Newton’s third law of motion, how are forces applied between two colliding hockey players?

What is momentum?

What does it mean that momentum is conserved?

2. Lab protocols should be followed, incorporating safety equipment. Goggles must be worn at all times.

3. Guide students to design investigations for Newton’s three laws. Allow students to examine the materials available. Alternately, you might be able to borrow field hockey or street hockey equipment from the physical education department for students to use in the gym, cafeteria, or parking lot. Following are some questions to help focus students’ plans:

What is true of a moving object? How can this tendency be shown by stopping an object

What law describes the behavior of a body acted on by a force?

How can this law be demonstrated with a constant force and constant mass?

What is true of a collision between bodies?

What will happen when bodies with unequal masses and equal velocities collide?

What will happen when bodies with unequal masses and unequal velocities collide?

4. The procedures suggested here are simple demonstrations of Newton’s three laws. However, students may prefer to construct other activities using these materials. For instance, to demonstrate Newton’s first law, a student walks at a constant, moderate speed and tries to drop a hockey puck onto a piece of tape on the floor. Dropping the puck when it is directly over the tape will not work. The student must drop the puck slightly before reaching the mark. The horizontal motion of the puck is unaffected by its vertical motion. Students should be encouraged to think of alternative ways this or other simple equipment they have can be used to demonstrate Newton’s laws.

5. Students may choose to use the toy car, hockey puck (or coins), and book for a simple demonstration of inertia. One student places the puck on top of the toy car and gently pushes it toward the book. The car will stop when it hits the book, but the puck will continue. Students record and analyze their results to explain how the law of inertia (Newton’s first law) is involved.

6. The skateboard and bricks comprise a body with a fixed mass. The spring scale allows students to measure a variable accelerating force. The meter stick, markers, and stop watches are needed to measure the speed of the accelerated body and the time the force acts. Students will need to practice pulling the loaded skateboard with a constant force. They can measure the final speed of the skateboard or its average speed while it is accelerating. Either method will demonstrate Newton’s second law.

7. Newton’s cradle demonstrates conservation of momentum for elastic collisions, because the steel spheres are highly elastic (unlike two colliding hockey players). The simplest case is seen by using only two spheres, and drawing them back the same distance before releasing them. The two have equal and opposite momenta, which are reversed during the collision. (It is not necessary to measure absolute speeds with Newton’s cradle. Students can judge relative speeds by comparing the distance a sphere swings before a collision to the distance of recoil after a collision.) A slightly more complex situation has two spheres with unequal velocities, and again the velocities are reversed during the collision. A large number of combinations of mass and velocity are possible if more spheres are used for the collisions, and students should be able to verify that momentum is conserved in all cases. They should be able to give a clear explanation of how conservation of momentum is related to Newton’s third law.

8. In areas where students are not involved with ice hockey, students could video record groups playing a few minutes of their favorite sport(s) and then analyze the motion in the video for examples of the three laws of motion and compare those with the motion in the ice hockey video.

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